let num: number = 100;
// num = 'qf001'
console.log(num);

let str: string = "qf001";
console.log(str);

let un: undefined = undefined;
console.log(un);

let nu: null = null;
console.log(nu);

let bo1: boolean = true;
let bo2: boolean = false;
console.log(bo1);
console.log(bo2);



let box: any = 100;
box = "qf001";
box = true;
box = undefined;
box = null;
box = [];
box = {};
box = () => {};